// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_
#define CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_

#include <stdint.h>

#include <deque>

#include "base/macros.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
#include "content/common/content_export.h"
#include "ipc/ipc_sender.h"

namespace blink {
namespace scheduler {
    class RendererScheduler;
}
}

namespace content {

// Utility class for throttling a stream of resource requests targetted to a
// specific IPC sender. The throttling itself is very basic:
//  * When there is no high-priority work imminent to the main thread, as
//    indicated by the RendererScheduler, throttling is disabled.
//  * When >= N requests have been sent in a given time window, requests are
//    throttled. A timer periodically flushes a portion of the queued requests
//    until all such requests have been flushed.
// TODO(jdduke): Remove this class after resource requests become sufficiently
// cheap on the IO thread, crbug.com/440037.
class CONTENT_EXPORT ResourceDispatchThrottler : public IPC::Sender {
public:
    // |flush_period| and |max_requests_per_flush| must be strictly positive
    // in duration/value.
    ResourceDispatchThrottler(IPC::Sender* proxied_sender,
        blink::scheduler::RendererScheduler* scheduler,
        base::TimeDelta flush_period,
        uint32_t max_requests_per_flush);
    ~ResourceDispatchThrottler() override;

    // IPC::Sender implementation:
    bool Send(IPC::Message* msg) override;

private:
    friend class ResourceDispatchThrottlerForTest;

    // Virtual for testing.
    virtual base::TimeTicks Now() const;
    virtual void ScheduleFlush();

    void Flush();
    void FlushAll();
    void LogFlush();
    bool ForwardMessage(IPC::Message* msg);

    base::ThreadChecker thread_checker_;

    IPC::Sender* const proxied_sender_;
    blink::scheduler::RendererScheduler* const scheduler_;
    const base::TimeDelta flush_period_;
    const uint32_t max_requests_per_flush_;

    base::Timer flush_timer_;
    base::TimeTicks last_flush_time_;
    uint32_t sent_requests_since_last_flush_;
    std::deque<IPC::Message*> throttled_messages_;

    DISALLOW_COPY_AND_ASSIGN(ResourceDispatchThrottler);
};

} // namespace content

#endif // CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_
